This invention relates to a focusing voltage adjusting circuit and a flyback transformer used for a television having a cathode ray tube (CRT) and a display apparatus, etc.
FIG. 1 shows a conventional focusing voltage adjusting circuit. In the figure, a high voltage transformer 1 has a primary coil L1 and a secondary coil L2 which is connected to a rectifier circuit consisting of a rectifier diode D1 and a smoothing capacitor C1, to produce a d.c. voltage Va.
A series circuit of resistors R1 and R2 and a variable resistor VR1 is connected to a secondary terminal of the transformer 1 at which the d.c. voltage Va appears. The mechanical variable resistor VR1 is used for adjusting a focusing voltage. This conventional focusing voltage adjusting circuit is installed in a flyback transformer 100 shown in FIG. 2 and the focusing voltage is adjusted with the variable resistor VR1 fixed on a surface of the transformer 100.
Since the conventional voltage adjusting circuit adjusts a focusing voltage with the mechanical variable resistor VR1, this conventional circuit cannot facilitate automatic focusing voltage adjustment and lacks reliability.
Further, it is impossible to adjust a focusing voltage on the front face of an apparatus such as a television and display apparatus due to a position of the high voltage transformer 1 installed therein. And, difficulty lies in adjustment of the focusing voltage because the high voltage transformer 1 cannot be freely installed in such an apparatus.